Oscillators, particularly quartz oscillators, are circuits that are used widely to provide a clock signal for microprocessors and memory components. An accurate duty cycle is often required here. The duty cycle of a clock signal is usually defined as the ratio between the time during which the clock signal is at a “high” level to the period of the full clock signal.
The document “High-Performance Crystal Oscillator Circuits: Theory and Application” by E. Vittoz, M. Degrauwe, and S. Bitz in the IEEE Journal of Solid-State Circuits, Volume 23, Number 3, June 1988, pp. 774 to 783 describes an equivalent circuit for an oscillator quartz and a quartz oscillator circuit.
Document U.S. Pat. No. 4,959,557 concerns a circuit with a feed-forward and a feedback branch for controlling the duty cycle of a clock signal.
Document U.S. Pat. No. 5,481,228 describes an arrangement for controlling the duty cycle using transistor stages connected in series.